In the search for high performance materials, considerable interest has been focused upon carbon fibers. The terms "carbon" fibers or "carbonaceous" fibers are used herein in the generic sense and include graphite fibers as well as amorphous carbon fibers. Graphite fibers are defined herein as fibers which consist essentially of carbon and have a predominant x-ray diffraction pattern characteristic of graphite. Amorphous carbon fibers, on the other hand, are defined as fibers in which the bulk of the fiber weight can be attributed to carbon and which exhibit an essentially amorphous x-ray diffraction pattern. Graphite fibers generally have a higher Young's modulus than do amorphous carbon fibers and in addition are more highly electrically and thermally conductive. It will be understood, however, that all carbon fibers, including amorphous carbon fibers, tend to include at least some crystalline graphite.
Industrial high performance materials of the future are projected to make substantial utilization of fiber reinforced composites, and carbon fibers theoretically have among the best properties of any fiber for use as high strength reinforcement. Among these desirable properties are corrosion and high temperature resistance, low density, high tensile strength and high modulus. During such service, the carbon fibers commonly are positioned within a solid continuous phase of a resinous matrix (e.g. a solid cured epoxy resin, polyimide resin, a high performance thermoplastic resin, etc.). Uses for carbon fiber reinforced composites include aerospace structural components, rocket motor casings, deep-submergence vessels, ablative materials for heat shields on re-entry vehicles, strong lightweight sports equipment, etc.
As is well known in the art, numerous processes have heretofore been proposed for the thermal conversion of organic polymeric fibrous materials (e.g. an acrylic multifilamentary tow) to a carbonaceous form while retaining the original fibrous configuration substantially intact. See, for instance, the following commonly assigned U.S. Pat. Nos. 3,539,295; 3,656,904; 3,723,157; 3,723,605; 3,775,520; 3,818,082; 3,844,822; 3,900,556; 3,914,393; 3,925,524; 3,954,950; and 4,020,273. During commonly practiced carbon fiber formation techniques a multifilamentary tow of substantially parallel or collimated carbon fibers is formed with the individual "rod-like" fibers lying in a closely disposed side-by-side relationship.
In order for the resulting carbon fibers to serve well as fibrous reinforcement within a continuous phase of resinous material, it is essential that the individual fibers be well dispersed within the matrix-forming resinous material prior to its solidification. Accordingly, it is essential when forming a composite article of optimum physical properties that the resinous material well impregnate the multifilamentary array of the carbon fibers so that resinous material is present to at least some degree between the individual fibers. If this does not occur, resin rich areas and voids will tend to be present in the resulting composite article.
See, the disclosures of U.S. Pat. Nos. 3,704,485; 3,795,944; 3,798,095; and 3,873,389 where the pneumatic spreading of carbon fibers was proposed prior to their resin impregnation. It has been found, however, that the pneumatic treatment of the carbon fibers to accomplish decollimation without spreading has tended to damage to an excessive degree the relatively delicate fibers frequently to the extent of fiber breakage, thereby creating an additional problem for those who choose to practice this additional process step and/or those carrying out the subsequent processing of the fibrous material.
In U.S. Pat. No. 4,466,949 is proposed a process for interconnecting ends of precursor yarns used in the production of carbon fibers through localized entanglement created by a fluid jet.
It has been recognized that the filaments of ordinary textile yarns can be interlaced or intermingled in order to improve their handling characteristics, etc. See, for instance, the disclosures of U.S. Pat. Nos. 2,985,995; 3,017,737; 3,110,151; 3,115,691; 3,262,179; 3,364,537; 3,563,021; 3,603,043; 3,701,248; 3,727,274; and 4,096,890.
It also has been recognized in the prior art that it has been necessary to apply a protective size to the surface of multifilamentary yarn bundles of carbon filaments prior to weaving the same to form a reinforcing fabric because of their extremely delicate nature. Different protective sizes sometimes are required for use with different matrix-forming resins, and in at least some instances the presence of even the best available protective sizes may be detrimental to the mechanical properties of the woven fabric reinforced composite article which ultimately is formed. For instance, the size may degrade upon exposure to highly elevated temperatures and/or otherwise may interfere with the adhesion between the reinforcing fibers and the matrix resin.
It is an object of the invention to provide an improved carbon fiber multifilamentary tow which is particularly suited for resin impregnation and resin retention.
It is an object of the invention to provide an improved carbon fiber multifilamentary tow which is particularly suited for impregnation with a matrix-forming resin to form a quality composite article.
It is an object of the invention to provide an improved carbon fiber multifilamentary tow wherein the individual filaments are randomly decollimated and commingled with numerous cross-over points (as specified) and are well adapted to receive and retain a matrix-forming resin.
It is an object of the present invention to provide an improved substantially void-free composite article comprising a solid resinous matrix material and the improved carbon fiber multifilamentary tow of the present invention incorporated herein as fibrous reinforcement.
It is an object of the present invention to provide an improved carbon fiber multifilamentary tow which is particularly suited for resin impregnation and in a preferred embodiment is substantially free of a size upon its surface.
It is an object of the present invention to provide an improved carbon fiber multifilamentary tow which in a preferred embodiment has been found to be capable of readily undergoing mechanized processing and handling in the absence of a protective size.
It is another object of the present invention to provide an improved process for weaving a fabric suitable for use as fibrous reinforcement in a resinous matrix material wherein the fabric incorporates a plurality of multifilamentary yarn bundles comprising adjacent substantially continuous carbonaceous filaments containing at least 70 percent carbon by weight.
It is a further object of the present invention to provide an improved woven fabric suitable for use as fibrous reinforcement in a resinous matrix material which incorporates a plurality of unsized multifilamentary yarn bundles comprising substantially continuous carbonaceous filaments containing at least 70 percent carbon by weight.
These and other objects, as well as the scope, nature, and utilization of the claimed invention will be apparent to those skilled in the art from the following detailed description and appended claims.